Novel cyanine dyes with fused imidazolo nuclei

ABSTRACT

NOVEL POLYMETHINE DYES ARE PROVIDED WHICH FEATURE AN IMIDAZOLE RING JOINED AT THE CARBON ATOM IN THE 5POSITION OF THE IMIDAZOLE RING TO A DIMETHINE LINKAGE, THE IMIDIAZOLE RING HAVING FUSED TO THE (A) SIDE THEREOF THE NON-METALLIC ATOMS REQUIRED TO COMPLETE AT LEAST ONE FUSED RING, AND A SECOND DESENSITIZING NUCLEUS JOINED AT A CARBON THEREOF TO THE DIMETHINE LINKAGE. THE INVENTION ALSO PROVIDES A NOVEL PHOTOGRAPHIC SILVER HALIDE EMULSIONS, INCLUDING DIRECT POSITIVES EMULSION CONTAINING THE DYES OF THE INVENTION.

United States Patent Olfice 3,809,691 Patented May 7, 1974 3,809,691NOVEL CYANINE DYES WITH FUSED IMIDAZOLO NUCLEI James W. Carpenter, JohnD. Mee, and Donald W. Heselfine, Rochester, N.Y., assignors to EastmanKodak Company, Rochester, N.Y.

No Drawing. Original application Oct. 23, 1967, Ser. No. 677,058, nowPatent No. 3,615,639, dated Oct. 26, 1971. Divided andthis applicationOct. 7, 1970, Ser.

Int. Cl. C09b 23/10 US. Cl. 260-240 E 12 Claims ABSTRACT OF THEDISCLOSURE Novel polymethine dyes are provided which feature animidazole ring joined at the carbon atom in the position of theimidazole ring to a dimethine linkage, the imidazole ring having fusedto the [a] side thereof the non-metallic atoms required to complete atleast one fused ring, and a second desensitizing nucleus joined at acarbon thereof to the dimethine linkage. The invention also providesnovel photographic silver halide emulsions, including direct positiveemulsions containing the dyes of the invention.

This application is a division of our copending application Ser. No.677,058, filed Oct. 23, 1967, now US. Pat. 3,615,639, granted Oct. 26,1971.

This invention relates to novel photographic materials, and moreparticularly to a new class of polymethine dyes, to intermediates andmethods for preparing these new dyes, to novel photographic emulsionscontaining these dyes, and to photographic elements prepared with suchemulsions.

It is known that direct positive images can be obtained withcertain'types of photographic silver halide emulsions. Many dyes whichhave been proposed as spectral sensitizers for direct positive emulsionshave various disadvantages, such as high D low speed, or undesiredspectral distribution in exposed areas. Some dyes proposed in the priorart are free from one or more of these disadvantages when the emulsionis fresh, but not during storage. There is a need in the art, therefore,for dyes which impart sensitivity primarily to blue or green radiation,have good stability on storage and are free from the abovedisadvantages.

It is, accordingly, an object of this invention to provide a new classof dyes that function as electron acceptors and spectral sensitizers forphotographic silver halide emulsions. l

Another object of this invention is to provide new and improved lightsensitive photographic emulsions, such as fogged, direct positiveemulsions, containing one or more of the new dyes of this invention.

A further object of this invention is to provide photographic elementscomprising a support having thereon at least one layer containing anovel light sensitive silver halide emulsion of this invention.

Another object is to provide means for the preparation of such noveldyes and photographic materials of this invention.

Other objects of this invention will be apparent from this disclosureand the appended claims.

We have now found that polymethine dyes derived from certain imidazoleshaving fused rings thereon, and containing desensitizing nuclei therein,are outstanding electron acceptors and spectral sensitizers in directpositive type photographic silver halide emulsions. They providesuperior reversal systems, especially with fogged silver halideemulsions, that are characterized by good speed and desired sensitivityto radiation in the green to red region of the spectrum, with maximumsensitivity occurring in most cases in the region of about 525-600 nm.Some dyes of the invention are especially useful as sensitizers for blueradiation. The images produced with these new direct positive emulsionsare clear and sharp, and of excellent contrast. In addition, the directpositive emulsions containing the novel dyes of this invention havebetter stability on storage than direct positive emulsions prepared withsensitizing dyes suggested in the prior art.

The new class of polyrnethine dyes of the invention include thosecomprising first and second 5- to 6-membered nitrogen containingheterocyclic nuclei joined by a dimethine linkage; the first of saidnuclei comprising an imidazole ring joined at the carbon atom in the 5-position (which is not necessarily the 5-position in the numbering ofthe compound) to said linkage, said imidazole ring having fused, on the[a] side thereof, the non-metallic atoms to complete at least one ringcontaining from 5 to 6 atoms; and said second nucleus being adesensitizing nucleus joined at a carbon atom thereof to said linkage.Reference should be made to Formulas I and II below for the numberingused for the imidazole ring. These numbers are generally not retained innumbering specific compounds, as will be apparent from the examples.

Some highly useful dyes of the invention include those comprising firstand second 5- to 6-membered nitrogen containing heterocyclic nucleijoined by a dimethine linkage; the first of said nuclei comprising animidazole ring joined at the S-carbon atom thereof to said linkage, saidimidazole ring having fused on the [a] side thereof the atoms tocomplete a nucleus selected from the group consisting of animidazo[l,2-a]pyridine nucleus, an imidazo- [2,l-a]thiazole nucleus, animidazo[2,l-b]oxazole nucleus, an imidazo[2,1,-b]selenazole nucleus, animidazo- [2,l-b]-l,3,4-thiadiazole nucleus; and said second nucleusbeing a desensitizing nucleus joined at a carbon atom thereof to saidlinkage.

The preferred polymethine dyes of the invention include thoserepresented by the following general formulas:

wherein n represents a positive integer of from 1 to 2, L represents amethine linkage, e.g., CH=, C(CH C(C H etc., R represents a hydrogenatom, an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl,hexyl, cyclohexyl, decyl, dodecyl, etc., or preferably an aryl group,e.g., phenyl, tolyl, xylyl, bromophenyl, chlorophenyl, nitrophenyl,methoxyphenyl, naphthyl, phenylazo phenyl, etc.; R and R each representsan alkyl group (including substituted alkyl), preferably a lower alkylgroup containing from 1 to 4 carbon atoms, e.g., methyl, ethyl, propyl,isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., an alkoxyalkyl group, e.g., B-methoxyethyl, w-butoxybutyl, etc., a hydroxyalkylgroup, e.g., flhydroxyethyl, w-hydroxybutyl, etc., a carboxyalkyl group,e.g., p-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g.,,B-sulfoethyl, 'y-sulfobutyl, w-sulfobutyl, etc. a sulfatoalkyl group,e.g., fl-sulfatoethyl, w-sulfatobutyl, etc. an acyloxyalkyl group, e.g.,S-acetoxyethyl, 'y-propionyL oxypropyl, w-butyryloxybutyl, etc., analkoxycarbonylalkyl, e.g., B-methoxycarbonylethyl,w-methoxycarbonylbutyl, etc., and the like, or an alkenyl group,e.g.,'allyl, 1-propeny1, 2-butenyl, etc., or an aryl group, e.g.,.phenyl, tolyl, xylyl, chlorophenyl, methoxyphenyl, naphthyl, etc., andthe like; X represents an acid anion, e.g., chloride, bromide, iodide,'thiocyanate, sulfamate, perchlorate, ptoluenesulfonate, methyl sulfate,ethyl sulfate, etc.; Z represents the non-metallic atoms necessary tocomplete a desensitizing heterocyclic nucleus selected from the groupincluding a nitrobenzothiazole nucleus, e.g., nitrobenzothiazole,6-nitrobenzothiazole, 5-chloro-6-nitrobenzothiazole, etc.; anitrobenzoxazole nucleus, e.g., 5- nitrobenzoxazole, 6 nitrobenzoxazole,5 chloro-6-nitrobenzoxazole, etc.; a nitrobenzoselenazole nucleus, e.g.,5- nitrobenzoselenazole, 6-nitrobenzoselenazole, 5-chloro-6-nitrobenzoselenazole, etc.; an imidazo[4,5-b]quinoxaline nucleus, e.g.,imidazo[4,5-b]quinoxaline, 1,3-dialkylimidazo[4,5-b]quinoxaline such as1,3-diethylimidazo[4,5-b] quinoxaline, 6chloro-1,3-diethy1imidazo[4,5-b]quinoxaline, etc.,1,3-dialkenylimidazo[4,5-b] quinoxaline such as1,3-diallylimidaZo[4,5-b] quinoxaline, 6-chloro-l,3-dia1lylimidazo[4,5-b1quinoxaline, etc., 1,3-diarylimidazo[4,5-b]quinoxaline such as 1,3-diphenylimidazo[4,5-b]quinoxaline,6-chloro-1,3-diphenylimidazo [4,5-b] quinoxaline, etc.; a3,3-dialkyl-3H-pyrrolo[2,3-b]pyridine nucleus, e.g., 3,3-dimethyl-3H-pyrrolo[2,3-b] pyridine, 3,3diethyl-3H-pyrrolo[2,3-b]pyridine, etc.; a 3,3-dialkyl-3H-nitroindole,e.g., 3,3-dimethyl 5 nitro-3H-indole, 3,3-diethyl-5-nitro- 3H-indole,3,3-dimethyl-6-nitro-3H-indole, etc.; a thiazolo- [4,5-b1quiuoline,nucleus; or a nitroquinoline, e.g., 5- nitroquinoline, 6-nitroquinoline,etc.; and Q represents the non-metallic atoms required to complete atleast one fused heterocyclic ring containing from 5 to 6 atoms in saidring, which ring may also contain a second or third hetero atom such asoxygen, sulfur, selenium or nitrogen such as a pyridine ring, e.g.,pyridine, an alkylpyridine such as a methylpyridine, and ethylpyridine,etc., a chloropyridine, a methoxypyridine, a nitropyridine, aphenylpyridine, etc. ring; a thiazole ring, e.g., thiazole,4-methylthiazole, S-methylthiazole, 4,5-dimethylthiazole, 4-pheny1-thiazole, 5-phenylthiazole, 4,5-diphenylthiazole, etc. ring; an oxazolering, e.g., oxazole, 4-methyloxazole, S-methyloxazole,4,5-dimethyloxazole, 4-phenyloxazole, 5-phenyloxazole, etc. ring; aselenazole ring, e.g., selenazole, 4- methylselenazole,S-methylselenazole, 4,5-dimethy1selenazole, 4-phenylselenazole,5-phenylselenazoe, etc. ring; a 1,3,4-thiadiazole ring, e.g.,1,3,4-thiadiazole, a 2-a1kyl- 1,3,4-thiadiazole such asZ-methyl-l,3,4-thiadiazole, etc., a 2-aryl-l,3,4-thiadiazole such as2-phenyl-1,3,4-thiadiazole, etc., Z-chloro-1,3,4-thiadiazole,2-nitro-1,3,4-thiadiazole, etc. ring; a pyridazine, e.g., pyridazine, analkylpyridazine such as 3-methylpyridazine, 3-butylpyridazine, etc., achloropyridazine such as 3-chloropyridazine, etc., an arylpyridazinesuch as 3-phenylpyridazine, 3,6-diphenylpyridazine, etc., analkoxypyridazine such as 4- ethoxypyrdazine, a quinoline ring, etc.Other desensitizing nuclei defined by Z in above Formula I that areuseful include nitrothiazole, nitronaphthothiazole, nitro-oxazole,nitronaphthoxazole, nitroselenazole, nitronaphthoselena zole, andnitropyridine, and the like. The monosalt dyes defined by Formula Iabove are particularly efficacious in photographic reversal processesand are preferred.

The polymethine dyes of the invention defined above are powerfulelectron acceptors for direct positive photographic silver halideemulsions. In addition, they are also useful in photographic silverhalide emulsions generally, for example as desensitizers in emulsionsused in the process described in Stewart and Reeves, U.S. Pat. No.3,250,618, issued May 10, 1966.

As used herein and in the appended claims, desensitizing nucleus refersto those nuclei which, when converted to a symmetrical carbocyanine dyeand added to gelatin silver chlorobromide emulsion containing 40 molepercent chloride and 60 mole percent bromide, at a concentration of from0.01 to 0.2 gram dye per mole of silver, caused by electron trapping atleast about an percent loss in the blue speed of the emulsion whensensitometrically exposed and developed three minutes in Kodak developerD19 at room. temperature. Advantageously, the desensitizing nuclei arethose which, when converted to a symmetrical carbocyanine dye and testedas just described, essentially completely desensitize the test emulsionto blue radiation (i.e., cause more than about to loss of speed to blueradiation).

The polymethine dyes defined by Formula I above are convenientlyprepared, for example, by heating a mixture of (1) a heterocycliccompound of the formula:

(III) Z wherein R and Q are as previously defined, in approxi matelyequimolar proportions, in a suitable solvent medium such as aceticanhydride. The crude dyes are then separated from the reaction mixturesand purified by one or more recrystallizations from appropriate solventssuch as ethanol, methanol, cresol/rnethanol mixtures, etc.

To prepare the dyes defined by Formula 11 above, a mixture of (1) acompound of above Formula III and (2) a compound of the formula:

d n R2N/ \C wherein R, R and Q are as previously defined, is reacted andthe purified dyes obtained in a manner similar to that described abovefor preparing the dyes of Formula I above.

The intermediates defined by Formula IV above are conveniently preparedby formulating a compound of the formula:

wherein R and Q are as previously defined, by the VHS- meier reactioncomprising treating with phosphoryl chloride in dimethylformamide,followed by hydrolysis with aqueous sodium hydroxide. After chilling,the precipitated crystals are collected, and washed well with water, andfurther purified, when necessary, by one or more recrystallizations fromsolvents such as acetone, ethanol, chloroform/ ethanol mixtures, and thelike. The salt intermediates defined by Formula V above are readilyprepared by quaternizing compounds represented by Formula IV above withany suitable quaternizing reagents, such as represented by methyliodide, dimethyl sulfate, diethyl sulfate, methyl p-toluenesulfonate,and the like.

In accordance with the invention, novel and improved direct positivephotographic silver halide emulsions are prepared by incorporating oneor more of the polymethine dyes of the invention into a suitable foggedsilver halide emulsion. The emulsion can be fogged in any suitablemanner, such as by light or with chemical fogging agents, e.g., stannouschloride, formaldehyde, thiourea dioxide and the like. The emulsion maybe fogged by the addition thereto of a reducing agent, such as thioureadioxide, and a compound of a metal more electropositive than silver,such as a gold salt, for example, potassium chloroaurate, as describedin British Pat. 723,019 (1955).

Typical reducing agents that are useful in providing such emulsionsinclude stannous salts, e.g., stannous chloride, hydrazine, sulfurcompounds such as thiourea dioxide, phosphonium salts such astetra(hydroxymethyl) phosphonium chloride, and the like. Typical usefulmetal compounds that are more electropositive than silver include gold,rhodium, platinum, palladium, iridium, etc., preferably in the form ofsoluble salts thereof, e.g., potassium chloroaurate, auric chloride, (NHPdCl and the like.

Useful concentrations of reducing agent and metal compound (e.g., metalsalt) can be varied over a considerable range. As a general guideline,good results are obtained using about .05 to 40 mg. reducing agent permole of silver halide and 0.5 to 15.0 mg. metal compound per mole ofsilver halide. Best results are obtained at lower concentration levelsof both reducing agent and metal compound.

The concentration of added dye can vary widely, e.g., from about 50 to2000 mg. and preferably from about 400 to 800 mg. per mole of silverhalide in the direct positive emulsions.

As used herein, and in the appended claims, fogged refers to emulsionscontaining silver halide grains which produce a density of at least 0.5when developed, without exposure, for 5 minutes at 68 F. in developerKodak DK-50 having the composition set forth below, when the emulsion iscoated at a silver coverage of 50 mg. to 500 mg. per square foot.

Water to make 1.0 liter.

The dyes of this invention are also advantageously incorporated indirect positive emulsions of the type in which a silver halide grain hasa water-insoluble silver salt center and an outer shell composed of afogged waterinsoluble silver salt that develops to silver withoutexposure. The dyes of the invention are incorporated, preferably, in theouter shell of such emulsions. These emulsions can be prepared invarious ways, such as those described in Berriman US. patent applicationSer. No. 448,467, filed Apr. 15, 1965, now US. Pat. 3,367,778, issuedFeb. 6, 1968. For example, the shell of the grains in such emulsions maybe prepared by precipitating over the core grains a light-sensitivewater-insoluble silver salt that can be fogged and which fog isremovable by bleaching. The shell is of suflicient thickness to preventaccess of the developer used in processing the emulsions of theinvention to the core. The silver salt shell is surface fogged to makeit developable to metallic silver with conventional surface imagedeveloping compositions. The silver salt of the shell is sufficientlyfogged to produce a density of at least about 0.5 when developed for 6minutes at 68 F. in Developer A below when the emulsion is coated at asilver coverage of 100 mg. per square foot. Such fogging can be effectedby chemically sensitizing to fog with the sensitizing agents describedfor chemically sensitizing the core emulsion, high intensity light andthe like fogging means well known to those skilled in the art. While thecore need not be sensitized to fog,

DEVELOPER A G. N-Methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0Potassium metaborate 35.0 Potassium bromide 1.0

Water to 1 liter. pH of 9.6.

Before the shell of water-insoluble silver salt is added to the silversalt core, the core emulsion is first chemically or physically treatedby methods previously described in the prior art to produce centerswhich promote the deposition of photolytic silver, i.e., latent imagenucleating centers. Such centers can be obtained by various techniquesas described herein. Chemical sensitization techniques of the typedescribed by Antoine Hautot and Henri Saubenier in Science et IndustriesPhotographiques, vol. XXVIII, January 1957, pp. 1-23 and January 1957,pp. 57-65 are particularly useful. Such chemical sensitization includesthree major classes, namely, gold or noble metal sensitization, sulfursensitization, such as by a labile sulfur compound, and reductionsensitization, e.g., treatment of the silver halide with a strongreducing agent which introduces small specks of metallic silver into thesilver salt crystal or grain.

The dyes of his invention are highly useful electron acceptors in highspeed direct positive emulsions comprising fogged silver halide grainsand a compound which accepts electrons, as described and claimed inIllingsworth US. patent application Ser. No. 609,794, filed Jan. 17,1967, and titled Photographic Reversal Materials III. The fogged silverhalide grains of such emulsions are such that a test portion thereof,when coated as a photographic silver halide emulsion on a support togive a maximum density of at least about one upon processing for sixminutes at about 68 F. in Kodak DK-50 developer, has a maximum densitywhich is at least about 30% greater than the maximum density of anidentical coated test portion which is processed for six minutes atabout 68 F. in Kodak DK-SO developer after being bleached for about 10minutes at about 68 F. in a bleach composition of:

Water to 1 liter.

The grains of such emulsions will lose at least about 25% and generallyat least about 40% of their fog when bleached for ten minutes at 68 F.in a potassium cyanide bleach composition as described herein. This fogloss can be illustrated by coating the silver halide grains as aphotographic silver halide emulsion on a support to give a maximumdensity of at least 1.0 upon processing for six minutes at about 68 F.in Kodak DK-50 developer and comparing the density of such a coatingwith an identical coating which is processed for six minutes at 68 F. inKodak DK-SO developer after being bleached for about 10 minutes at 68 F.in the potassium cyanide bleach composition. As already indicated, themaximum density of the unbleached coating will be at least 30% greater,generally at least 60% greater, than the maximum density of the bleachedcoating.

The silver halides employed in the preparation of the photographicemulsions useful herein include any of the photographic silver halidesas exemplified by silver 'bromide, silver iodide, silver chloride,silver chlorobromide, silver bromoiodide, silver chlorobromide, and thelike. Silver halide grains having an average grain size less than aboutone micron, preferably less than about 0.5 micron, give particularlygood results. The silver halide grains can be regular and can be anysuitable shape such as cubic or octahedral, as described and claimed inIllingsworth US. patent application Ser. No. 609,778, filed Jan. 17,1967, and titled Direct Positive Photographic Emulsions I. (US. patentapplication Ser. No. 609,778 is a continuation-in-part of US. patentapplication, Ser. No. 533,400, filed Mar. 11, 1966; and US patentapplication, Ser. No. 619,909, filed Mar. 2, 1967, now U.S. Pat.3,501,306, issued Mar. 17, 1970 is a continuation-in-part of Ser. No.533,400.) Such grains advantageously have a rather uniform diameterfrequency distribution, as described and claimed in Illingsworth US.patent application Ser. No. 609,790, filed Ian. 17, 1967, and titledPhotographic Reversal Emulsion II. (US. patent application, Ser. No.609,790 is a continuation-in-part of US. patent application Ser. No.533,440, filed Mar. 11, 1966; and U.S. patent application Ser. No.619,948, filed Mar. 2, 1967, now US. Pat. 3,501,305, issued Mar. 17,1970 is a continuation-in-part of Ser. No. 533,440.) For example, atleast 95%, by weight, of the photographic silver halide grains can havea diameter which is within about 40%, preferably within about 30% of themean grain diameter. Mean grain diameter, i.e., average grain size, canbe determined using conventional methods, e.g., as shown in an articleby Trivelli and Smith entitled Empirical Relations Between Sensitometricand Size-Frequency Characteristics in Photographic Emulsion Series inThe Photographic Journal, vol. LXXIX, 1949, pp. 330-338. The foggedsilver halide grains in these direct-positive photographic emulsions ofthis invention produce a density of at least 0.5 when developed withoutexposure for five minutes at 68 F. in Kodak DK-50 developer when such anemulsion is coated at a coverage of 50 to about 500 mg. of silver persquare foot of support. The preferred photographic silver halideemulsions comprise at least 50 mole percent bromide, the most preferredemulsions being silver bromoiodide emulsions, particularly thosecontaining less than about ten mole percent iodide. The photographicsilver halides can be coated at silver coverages in the range of about50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes of theinvention are advantageously incorporated in the washed, finished silverhalide emulsion and should, of course, be uniformly distributedthroughout the emulsion. The methods of incorporating dyes and otheraddenda in emulsions are relatively simple and well known to thoseskilled in the art of emulsion making. For example, it is convenient toadd them from solutions in appropriate solvents, in which case thesolvent selected should be completely free from any deleterious effecton the ultimate light-sensitive materials. Methanol, isopropanol,pyridine, water, etc., alone or in admixtures, have proven satisfactoryas solvents for this purpose. The type of silver halide emulsions thatcan be sensitized with the new dyes include any of those prepared withhydrophilic colloids that are known to be satisfactory for dispersingsilver halides, for example, emulsions comprising natural materials suchas gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. andhydrophilic synthetic resins such as polyvinyl alcohol, polyvinylpyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate,and the like.

The binding agents for the emusion layer of the photographic element canalso contain dispersed polymerized vinyl compounds. Such compounds aredisclosed, for example, in US. Pats. 3,142,568; 3,193,386; 3,062,674 and3,220,844 and include the water insoluble polymers of alkyl acrylatesand methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylatesand the like.

' The dyes, reducing agents and metal compounds of the invention can beused with emulsions prepared, as indicated above, with any of thelight-sensitive silver halide salts including silver chloride, silverbromide, silver chlorobromide, silver bromoiodide, silverchlorobromoiodide, etc. Particularly useful are direct positive foggedemulsions in which the silver salt is a silver bromohalide comprisingmore than 50 mole percent bromide. Certain dyes of this invention arealso useful in emulsions which contain color formers.

The novel emulsions of this invention may be coated on any suitablephotographic support, such as glass, film base such as celluloseacetate, cellulose acetate butyrate, polyesters such as poly(ethyleneterephthalate), paper, baryta coated paper, polyolefin coated paper, e.g., polyethylene or polypropylene coated paper, which may be electronbombarded to promote emulsion adhesion, to produce the novelphotographic elements of the invention.

The preparation of the highly useful polymethine dyes of the inventionderived from imidazo[l,2-a]pyridines, and certain intermediatestherefor, are illustrated by the following examples.

EXAMPLE 1 3-ethyl-6-nitro-2- 2- (-phenylimidazo 1,2-a] pyrid-3 -yl)vinyl] benzothiazolium iodide can,

can 1 3 formyl Z-phenylimidazo[1,2-a]pyridine 1.11 g., 1 mol.) and3-ethyl-2-methyl-6-nitrobenzothiazolium ptoluenesulfonate (1.98 g., 1mol.) in acetic anhydride (10 ml.) are heated at reflux for 5 minutes.The cooled mixture is diluted with ether. The ether layer is decantedand the sticky residue dissolved in hot methanol (25 ml.). A solution ofsodium iodide (2.0 'g.) in a little water is added, the mixture chilled,and the solid collected. After two recrystallizations from methanol, theyield of purified dye is 0.60 g. (21% M.P. greater than 179 C.

The above prepared dye containing the desensitizing 3-ethyl-6-nitrobenzothiazole nucleus is photographically tested for itsusefulness as an electron acceptor and spectral sensitizer for foggeddirect positive photographic silver halide emulsions by the followingprocedure.

A gelatin silver bromoiodide emulsion (2.5 mole percent of the halidebeing iodide) and having an average grain size of about 0.2 micron isprepared by adding an aqueous solution of potassium bromide andpotassium iodide, and an aqueous solution of silver nitrate,simultaneously to a rapidly agitated aqueous gelatin solution at atemperature of 70 C., over a period of about 35 minutes. The emulsion ischill-set, shredded and washed by leaching with cold water in theconventional manner. The emulsion is reduction-gold fogged by firstadding 0.2 mg. of thiourea dioxide per mole of silver and heating for 60minutes at 65 C. and then adding 4.0 mg. of potassium chloroaurate permole of silver and heating for 60 minutes at 65 C. The dye of the aboveexample, 3- ethyl 6 nitro 2 [2 (2 phenylimidazo[l,2-a]pyrid-3-yl)vinyl]benzothiazolium iodide is then added to the abovefogged emulsion in amount sufficient to give a concentration of 0.08gram of the dye per mole of silver. The resulting emulsion is coated ona cellulose acetate film support at a coverage of mg. of silver and 400mg. of gelatin per square foot of support.

A sample of the coated support is then exposed on an Eastman Ibsensitometer using a tungsten light source and processed for 6 minutesat room temperature in Kodak D-19 developer which has the followingcomposition:

Water to make 1.0 liter.

then fixed, washed and dried. The results are listed in Table Ihereinafter. Referring thereto, it will be seen that the dye of thisexample has a maximum density in the unexposed areas of 1.87 and aminimum density in exposed areas of 0.12, a maximum sensitivity of 550nm. and a relative speed of 339. This result indicates that the dyecompound of the above example is well suited to function as both anelectron acceptor and spectral sensitizer. It thus provides excellentquality direct positive photographic silver halide emulsions. Excellentmagenta images are obtained when the color former1(2,4,6-trichlorophenyl) 3 {3 [(2,4-di-tert-phenylphenoxy)acetamido]benzimido}-2-pyrazolin-S-one is incorporated in the emulsionof this example, the emulsion is coated on a support, exposed to atungsten source through Wratten filter No. 61 and No. 16, and reversalprocessed as described in Graham et al. U.S. Pat. 3,046,129, issued July24, 1962, in Example (a), col. 27, lines 27 et seq. except thatblack-and-white (MQ) development is omitted, the color development isreduced to one minute and is conducted in total darkness until afterfixing.

EXAMPLE 2 1,3-diphenyl-2- [2- (2-phenylimidazo 1,2-a] pyrid-3 -yl)vinyl] imidazo [4,5 -b] quinoxalinium iodide l N N /N\ r k-orpon $1 CamI This dye is prepared in a similar manner to that described for Example1, except that 2-methyl-1,3-diphenylimidazo[4,5-b] quinoxaliniump-toluenesulfonate (2.54 g., 1 mol.) is used in place of3-ethyl-2-methy1-6-nitrobenzothiazolium p-toluenesulfonate. After tworecrystallizations from cresol/methanol, the yield of purified dye is0.83 g. (25% M.P. 300 C.

The above dye containing the desensitizing nucleus 1,3-diphenylimidazo[4,5-b] quinoxaline nucleus is photographically tested bythe exact procedure of above Example 1. The results as shown in Table Ihereinafter indicate that this dye qualifies as a good electron acceptorand spectral sensitizer for fogged direct positive photographicemulsions. The densities are shown to be 1.91 and 0.05 for the unexposedand exposed areas, respectively, with a maximum sensitivity at 550 nm.and a relative speed of 468.

EXAMPLE 3 3 ethyl 2-[2 (1 methyl-Z-phenyl-lH-imidazo[1,2-a] pyridinium 3yl)vinyl] 6 nitrobenzothiazolium diiodide 3 formyl 1 methyl 2 phenyl1H-imidazo[1,2-a] pyridinium iodide (1.32 g., 1 mol.) and3-ethyl-2-methyl- 6-nitro benzothiazolium p-toluenesulfonate (1.98 g., 1mol.) in cresol (10 ml.) are heated at reflux for 1 minute. 47% aqueousHI (2 ml.) is added to the cooled mixture,

then excess ether added. The solid is collected. After tworecrystallizations from cresol/methanol, the yield of purified dye is0.44 g. (13%), M.P. 257 C., decomposes.

The above dye containing the desensitizing nucleus 3-ethyl-G-nitrobenzothiazole nucleus, as well as having two quaternarynitrogen atoms (defined by Formula II above), are tested by the exactprocedure described in above Example 1. The results as shown in Table Ihereinafter indicate that this dye does produce moderately goodreversal, having densities of 1.43 and 0.13 for the unexposed andexposed areas, respectively, with a relative speed of 138. However, thespectral sensitization is limited to the blue region of the spectrum.

EXAMPLE 4 2 [2 (1 methyl 2 phenyl 1H imidazo[1,2-a] pyridinium 3yl)vinyl 1,3 diphenylimidazo [4,5-b] quinoxalinium di-iodide CuHs 3formyl-1-methy1-2-phenyl-1H-imidazo 1,2-a] pyridinium iodide (1.32 g., 1mol.) and 2-methy1-1,3-diphenylimidazo[4,5-b]quinoxaliniump-toluenesulfonate (1.40 g., 1 mol.) in acetic anhydride are heated atreflux, with constant stirring, for 5 minutes. The cooled mixture isdiluted with ether and the ether layer decanted. The residue isdissolved in methanol (50 ml.) and a solution of sodium iodide (1.0 g.)in a little water added. The mixture is chilled and the solid collected.After two recrystallizations from cresol/methanol, the yield of purifieddye is 0.49 g. (22% M.P. 300 C.

Photographic testing of the above dye containing the desensitizing 1,3diphenylimidazo[4,5-b]quinoxaline nucleus, by the procedure described inabove Example 1, indicates that it possesses moderate reversalproperties showing densities of 1.80 and 0.72 for the unexposed andexposed areas, respectively, with sensitization limited to just the blueregion of the spectrum and a relative speed of 50. It will be noted thatthis dye also contains two quaternary nitrogen atoms and is defined byFormula 11 above.

EXAMPLE 5 3-ethy1-2-{2-[8-methyl-2-(4-nitrophenyl) imidazo[1,2-a]pyrid-3-yl]vinyl}-6-nitrobenzothiazolium iodide This dye is prepared andpurified in a similar manner to that described for Example 1, exceptthat 3-formyl-8- methyl 2-(4-nitrophenyl)imidazo[1,2-a]pyridine issubstituted for the pyridine compound specified in Example 1. The yieldof purified dye is 0.78 g. (25%), M.P. 315 C.

The above dye is photographically tested by the exact proceduredescribed in above Example 1 and found to be an excellent electronacceptor and spectral sensitizer for fogged direct positive photographicemulsions. Reference to Table I hereinafter, shows that this dye givesdensities 1 1 of 1.96 and 0.02 for the unexposed and exposed areas,respectively, with a maximum sensitivity at 585 nm. and a relative speedof 575.

EXAMPLE 6 1,3-diethyl-2-{2- S-methyl-Z- 4-nitrophenyl imidazo 1,2-

a] pyrid 3 yl]vinyl}imidazo[4,5-b]quinoxalinium ptoluenesulfonate bzHs 3formyl 8-methyl-2-(4-nitrophenyl)imidazo[1,2-a] pyridine (1.41 g., 1mol., 2 methyl-1,3-diethylimidazo [4,5-b]quinoxaliniurnp-toluenesulfonate (2.06 g., 1 mol.) and acetic anhydride (20 ml.) aremixed together, re fluxed for 30 minutes, chilled and added slowly toethyl ether (1 1.). The reddish-orange precipitate, which forms, iscollected by filtration. After two recrystallizations from methanol, theyield of purified dye is 1.16 g. (34%), M.P. 282-7 C., decomposes.

The above dye containing the desensitizing1,3-diethylimidazo[4,5-b]quinoxaline nucleus is photographically testedfor reversal properties by the exact procedure described in aboveExample 1. The results as shown in Table I hereinafter indicate thatthis dye is an excellent electron acceptor and spectral sensitizer forfogged direct positive photographic emulsions. The densities are shownto be 1.98 and 0.02 for the unexposed and exposed areas, respectively,with a maximum sensitivity at 560 and a relative speed of 692. It willbe apparent that other salts of this dye such as the cholride, bromide,iodide, perchlorate, methylsulfate, etc. can be readily prepared andthat such salts will also be similarly useful in direct positiveemulsions.

EXAMPLE 7 6-chloro-2-{2-[8-methyl-2-(4-nitrophenyl)imidazo[1,2-a]pyrid-3-yl] vinyl}-- 1,3-diphenylimidazo [4,5 -b] quinoxalinium iodide Amixture of 3 formyl 8-methyl-2-(4-nitrophenyl) imidazo[1,2-a]pyridine(1.41 g., 1 mol.), 6-chloro-1,3-di phenylimidazo[4,5-b]quinoxalinium ptoluenesulfonate (2.71 g., 1 mol.) and acetic anhydride (20 ml., 40mol.) are refluxed for 10 min., cooled and added with stirring to ethylether (1 1.). The precipitate is collected by suction filtration, washedwith ethyl ether and dried; yield 3.28 g. (81%). The p-toluenesulfonatesalt is converted to the iodide by dissolving in methanol (100 ml.),treating with sodium iodide (2.0 g.), heating to the boiling point,cooling, filtering, washing with methanol and dryig at 100 C. in vacuofor 4 hrs., yield 1.96 g. (51%).

12 The iodide is recrystallized from methanol (410 ml./g.); yield 0.70g. (18%), M.P. 310 C., decomposes.

The above prepared dye containing the desensitizing1,3-diphenylimidazo[4,5-b]quinoxaline nucleus is tested by the procedureof above Example 1. The results shown in Table I hereinafter indicatethat this dye is an outstanding electron acceptor and spectralsensitizer for fogged direct positive photographic emulsions. Thedensities are 1.74 and 0.04 for the unexposed and exposed areas,respectively, the maximum sensitivity is at 595, and the relative speedis 1050.

EXAMPLE 8 1,3,3-trimethy1-2-{2-[S-methyl 2(4-nitrophenyl)imidazo[1,2-a]pyrid 3 yl]vinyl}-5-nitro-3H-indoliumptoluenesulfonate 01% /CH: CH: C

N NO:

CH=CH- 6 III 9 0 s 0,0711, CH;

A mixture of 3-formyl-8-methyl-2-(4-nitrophenyl) imidazo[1,2-a]pyridine(1.41 g., 1 mol.), 1,2,3,3-tetramethyl-5-nitro-3H-indoliump-toluenesulfonate (1.95 g., 1 mol.) and acetic anhydride (20 ml., 40mol.) is refluxed for 2 /2 min., cooled and added with stirring to 1 l.of ethyl ether. The precipitate is collected by suction filtration,washed with ethyl ether and dried; yield 2.98 g. (91% The dye isrecrystallized from methanol ml./ g.) and dried; yield 2.39 g. (73%),M.P. 253255 C., decomposes.

The above dye containing the 1,3,3-trimethyl-5-nitro- 3H-ind0linenucleus is tested by the procedure of above Example 1. The results areshown in Table I hereinafter. Referring thereto, the densities are 1.88and 0.04 for the unexposed and exposed areas, respectively, with amaximum sensitivity at 580 nm. and a relative speed of 955. Accordingly,this dye is also an outstanding electron acceptor and spectralsensitizer for fogged direct positive photographic emulsions.

EXAMPLE 9 1,3,3-trimethyl-2-{2-[S-methyl 2 (4-phenylazophenyl)imidazo[1,2-a]pyrid 3 yl]vinyl}-5-nitro-3H-indolium p-toluenesulfonateCH CH 3-formyl-8-methyl 2 (4 phenylazophenyl)imidazo [1,2-a]pyridine(1.00 g., 1 mol.) and l,2,3,3-tetramethyl 5-nitro-3H-indoliump-toluenesulfonate (1.15 g., 1 mol.)

in acetic anhydride (25 ml.) are refluxed for 10 minutes. The cooledreaction mixture is added to ether (300 ml.), stirred and filtered; theprecipitate is re-suspended in ether (300 ml.), recovered by filtration,and dried; yield 1.84 g. (92%). The dye is purified by recrystallizationfrom 3-ethyl 2 {2-[8-methy1-2-(4-phenylazophenyl)imidazo[1,2-a]pyrid-3-yl]vinyl} 6 nitrobenzothiazolium ptoluenesulfonate S:ONQ. N

C Habra. o s 0.01111 C H: C H

3-formyl 8 methyl-2-(4-phenylazophenyl)imidazo [1,2-a1pyridine (1.00 g.,1 mol.) and 3-ethyl-2-methyl-6- nitrobenzothiazolium p-toluenesulfonate(1.15 g., 1 mol.) in acetic anhydride (25 ml.) are refluxed for 15minutes. The cooled reaction mixture is added to ether (500 ml.),stirred and filtered; the precipitate is re-suspended in ether (500ml.), recovered by filtration, washed with ether and dried; yield 1.71g. (82%). The dye is purified by recrystallization from ethanol (225ml.); yield 0.53 g. (26%), MP. 194-196 C., decomposes.

The above dye containing the desensitizing 3-ethyl-6 nitrobenzothiazolenucleus is tested for reversal properties by the exact procedure ofabove Example 1. The results shown in Table I hereinafter indicate thatthis dye is a moderately good electron acceptor and spectral sensitizerfor fogged direct positive photographic emulsions. The densities are1.64 and 0.10 for the unexposed and exposed areas, respectively, with amaximum sensitivity at 586 nm. and a relative speed of 501.

EXAMPLE 11 3 formyl 8 methyl-2-(4-phenylazophenyl)imidazo[1,2-a1pyridine (1.00 g., 1 mol.) and1,3-diethyl-2-methylimidazo[4,5-b]quinoxalinium p-toluenesulfonate (1.19g., 1 mol.) in acetic anhydride (25 ml.) are refluxed for minutes. Thechilled reaction mixture is added to ether (300 ml.), stirred andfiltered; the precipitate is re-suspended in ether (300 ml.), recoveredby filtration, washed with ether and dried; yield 1.58 g. (74%). The dyeis purified by recrystallization from ethanol (250 m1.); yield 0.46 g.(23%), MP. 238-240 C.

The above dye containing the desensitizing1,3-diethylimidazo[4,5-b]quinoxaline nucleus is found to be a moderatelygood electron acceptor and spectral sensitizer for photographic reversalsystems by the test procedure of above Example 1. Table I lists theresults of this test.

Reference thereto shows densities of 1.72 and 0.08 for the unexposed andexposed areas, respectively, with a grgarirnum sensitivity at 580 nm.and a relative speed of EXAMPLE 12 1,3-diethyl-2-{2-[7-methyl 2(4-nitrophenyl)imidazo [1,2-a]pyrid-3-yl]vinyl}imidazo[4,5bJquinoxalinium p-toluenesulfonate Ii 1. -(tn CzH5 N02 osmour,

This dye is prepared in the same manner as the dye of above Example 11,except that 3-methyl-7-methyl-2- (4nitrophenyl)imidazo[1,2-a]pyridine issubstituted for the pyridine compound of Example 11. The yield of dye is1.42 g. (42%), MP. 293-296" C.

This dye containing the desensitizing 1,3-diethylimidazo[4,5-b]quinoxaline nucleus is photographically tested by the proceduredescribed in Example 1. The results as shown in Table I hereinafterindicate that this dye is an outstanding electron acceptor and spectralsensitizer for foggcd direct positive photographic emulsions. Thedensities are shown to be 1.92 and 0.03 for the unexposed and exposedareas, respectively, with a maximum sensitivity at 575 nm. and arelative speed of 1380.

EXAMPLE 13 6-chloro-2-{2-[7-methyl-2- (4 nitrophenyl)imidazo[1,2-a]pyrid 3 yl]vinyl} 1,3 diphenylimidazo[4,5-b] quinoxalinium iodide Thisdye is prepared in the same manner as the dye of Example 11, except thatthe reactants are 3-formyl-7- methyl-Z- (4-nitropheny1) imidazo 1,2-a]pyridine and 6 chloro 1,3 diphenylimidazo[4,5-b1quinoxaliniumptoluenesulfonate. The p-toluenesulfonate salt is converted to theiodide by treatment with sodium iodide. The yield of dye is 0.58 g.(15%), M.P. 315 C.

The above dye containing the desensitizing 6-chloro-1,3-diphenylimidazo[4,5-b]quinoxaline nucleus is tested and found to bean outstanding electron acceptor and spectral sensitizer for foggeddirect positive photographic emulsions. The results of the test by theprocedure described in above Example 1 are listed in Table Ihereinafter. The densities are 1.84 and 0.06 for the unexposed andexposed areas, respectively, with a maximum sensitivity at 600 nm. and arelative speed of 1510.

15 EXAMPLE 14 1,3,3-trimethyl-2-{2-[7 methyl-2-(4nitrophenyl)imidazo[1,2-a]pyrid 3 yl]vinyl}--nitro-3H-indoliumptoluenesulfonate CH3 CH3 N N02 N CH=CH N EH3 o s 0.07m

This dye is prepared in the same manner as the dye of Example 11, exceptthat the reactants are 3-formyl-7-methyl-2-(4-nitrophenyl)imidazo[1,2-a]pyridine and 1,2,3,3-tetramethyl-5-nitro-3H-indolium p-toluenesulfonate. The yield of dyeis 1.13 g. (35%), M.P. 227229 C., decomposes.

The above dye containing the desensitizing1,3,3-trimethyl-5-nitro-3H-indole nucleus is tested by the exactprocedure described in above Example 1. The results as shown in Table Ihereinafter indicate that this dye is also an outstanding electronacceptor and spectral sensitizer for fogged direct positive photographicemulsions. The densities are 1.93 and 0.06 for the unexposed and exposedareas respectively, with a maximum sensitivity at 590 nm. and a relativespeed of 1200.

It will be apparent from the foregoing that the intermediates employedin above dye Examples 1 to 14 can be substituted by any other of thosedefined by Formula III above to give the corresponding dyes havinggenerally similar properties as electron acceptors and spectralsensitizers for fogged direct positive photographic emulsions, forexample, the dye l-alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl,decyl, etc.)-6-nitro-2 [3 (2 phenylimidazo[ 1,2-a]pyrid-3-yl)vinyl]benzoxazolium salt (e.g., the chloride, bromide,iodide, perchlorate, p-toluenesulfonate, etc. salt); the dye l-alkyl-(e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl, etc.)-6-nitro 2[3 (2- phenylimidazo[1,2-a]pyrid 3 yl)vinyl] selenazolium salt (e.g.,the chloride, bromide, iodide, perchlorate, p-toluenesulfonate, etc.salt); the dye 1,3-dialkyl (e.g., wherein alkyl is methyl, ethyl,propyl, isopropyl, butyl, decyl, etc.)- 2-{2-7-(or 8-)methyl-2-(4-nitrophenyl)imidazo[1,2 a] pyrid-3-yl]vinyl}imidazo[4,5b]quinoxaliuium salt (e.g., the chloride, bromide, iodide, perchlorate,p-toluenesulfonate, etc. salt); the dye 1,3-diallyl-2-{2 [8 methyl 2-(4-nitrophenyl)imidazo[l,2-a]pyrid 3 yl]vinyl}imidazo-[4,5-b1quinoxalinium salt (e.g., the chloride, bromide, iodide,perchlorate, p-toluenesulfonate, etc. salt); the dye 1,3-dialkyl (e.g.,wherein alkyl is methyl, ethyl, propyl, isopropyl, butyl, decyl,etc.)-6-chloro 2 {2 [7 (or8-)-methyl2-(4-nitrophenyl)imidazo[1,2-a]pyrid 3 yl]vinyl}-imidazo[4,5-b]quinoxalinium salt (e.g., the chloride, bromide,iodide, perchlorate, p-toluenesulfonate, etc. salt), and the like. Theimidazo[1,2-a]pyridine intermediates employed in the above dye Examples1 to 14 can also be substituted by any other of those defined byFormulas IV and V to give the corresponding dyes having generallysimilar properties as electron acceptors and spectral sensitizers infogged direct positive photographic emulsions.

The following Examples 15 to 23 illustrate'the preparations of a numberof intermediates defined by Formulas 1V and V.

16 EXAMPLE 1s 2-phenylimidazo 1,2-a] pyridine 2-bromoacetophenone (19.9g., 1 mol.), 2 aminopyridine (1.17 g., 1.2 mol.) and sodium bicarbonate(13.1 g., 1.56 mol.) in ethanol ml.) are stirred together at roomtemperature for 3 hours, then heated at reflux for a further 1 hour. Themixture is cooled and diluted to 500 ml. with water. The solid whichseparates is collected and then washed with water. The yield was 17.5 g.M.P. 137 C. (lit. 6 C.) (Kaye, Parris and Burlant, J.A.C.S., 75, 746).

EXAMPLE 16 8-methyl-2- (4-nitrophenyl imidazo 1,2-a] pyridine I Clh2-amino-3-methylpyridine (5.41 g., 2 mol.), 2-bromo-4'-nitroacetophenone (12.20 g., 2 mol.), sodium carbonate (2.65 g., 1mol.) and ethanol (50 ml.) are mixed together and stirred at roomtemperature for 24 hours. The precipitate is collected by filtration,washed twice with distilled water (400 ml.) and air dried; yield 9.67 g.(76% M.P. 160 C. (lit. M.P. 168171 C.); Ann. Chim.

(Rome) 54,496 (1964), Mattu and Marongiu.

EXAMPLE 17 3-formyl-2-phenylimidazo 1,2-a pyridine This compound isprepared in a similar manner to that described for Example 17. The yieldis 9.30 g. (87%). M.P. 215-19 C., decomposes.

17 18 EXAMPLE 19 EXAMPLE 23 3-formyl-1-methy1-2-phenyl-lH-imidazo 1,2-a]pyridinium 3401' -p f l p y imidaZO- iodide [1,2-a]pyr1d1ne 5 CH0 CH0 Na CBHQ \N N CH; (3H1 I This compound is synthesized in the same manneras 3-formyl 2 phenylimidazo[1,2-a]pyridine (1.11 g., 1 mol.) isdissolved in hot dimethylformamide (2 m1.) and the solution cooledrapidly to give a slush. Methyl iodide (2.8 g., 4 mol.) is added and themixture heated at a gentle reflux for /2 hour, as solid separated. Themixture is cooled and diluted with ether. The solid is collected andwashed with ether. Yield 1.25 g. (95%), M.P. 2269 C., decomposes.

EXAMPLE 7 -methyl-2- (4-nitrophenyl) imidazo 1,2-a] pyridine Thiscompound is made in the same manner as the 8- methyl derivative (Example16); yield 10.59 g. (84%), M.P. 204207 C. The material is purified byrecrystallization from ethanol 1.1 1.); yield 8.08 g. (64%), M.P.219-221 C., decomposes (lit. M.P. 220 C.; CA, 62, 118010 (1965).

EXAMPLE 2-1 8-methy1-2-(4-phenylazophenyl) imidazo 1 ,2-a] pyridine fiedby recrystallization from ethanol (800 ml.), 7.70 g. (49%, M.P. 193-195C., decomposes.

EXAMPLE 22 3-formy1-7-methyl-2- (4nitrophenyl) imidazo 1,2-a] pyridineCHO N f l N This compound is synthesized in the same manner as the8-methyl derivative (Example 18); yield 8.29 g. (98%). The product ispurified by recrystallization from chloroform-acetone; yield 5.87 g.(70%), M.P. 2-67268 C., decomposes.

the 4-nitrophenyl derivatives; yield 7.85 g. (89%). The product isrecrystallized twice from ethanol; yield 3.31 g. (37%), M.P. 165 C.,decomposes.

It will be apparent that still other intermediates defined by FormulasIV and V above can be readily prepared by appropriate substitutions inthe procedures of above Examples 15 to 23.

The preparation of the highly useful polymethine dyes of the inventionderived from imidazo[2,l-b]thiazoles, and intermediates therefor, isillustrated by the following examples.

EXAMPLE 24 1,3,3 trimethyl-5-nitro-2-{2-[6-(4-nitrophenyl)imidazo- [2,1-b]thiazol-5-yl] vinyl} 3H-indolium p-toluenesulfonate cm Cm NQ N02\2-CH=CH\ ea (in.

osolcm,

5 formyl 6 (4-nitrophenyl)imidazo[2,1-b]thiazole (1.37 g., 1 mol.) and1,2,3,3-tetramethyl-5-nitro-3H-indolium p-toluenesulfonate (1.95 g., 1mol.) in acetic anhydride are refluxed for several minutes. The cooledreaction mixture is added to ether (1 1.), stirred and filtered; theprecipitate is washed with ether and dried; yield 2.49 g. (77%). The dyeis purified by recrystallization from methanol (500 ml.); yield 0.93 g.(29%), M.P. 247- 248 C., decomposes.

' This dye containing the desensitizing 1,3,3-trimethyl-5-nitro-3H-indole nucleus is tested by the exact procedure described inabove Example 1. The results in Table 1 hereinafter indicate that thisdye is an excellent electron acceptor and spectral sensitizer for foggeddirect positive photographic emulsions. The densities are 1.82 and 0.04for the unexposed and exposed areas, respectively, with a maximumsensitivity at 580 nm. and a relative speed of 832.

EXAMPLE 25 1,3diethyl-2-{2-[6-(4-nitrophenyl)imidazo[2,l-b]thiazol-S-yl] vinyl}imidazo[4,5-b] quinoxalinium p-toluene- This compound is prepared in a mannersimilar to Example 24; yield 2.97 g. (91%). The dye is purified byrecrystallization from methanol (380 ml.); yield 0.81 g. (25% M.P.290292 C., decomposes.

The above prepared dye containing the desensitizing imidazo[4,5-b]quinoxaline nucleus is tested as described in above Example 1. Theresults are listed in the following Table 1. Referring thereto it willbe seen that this dye qualifies as an outstanding electron acceptor andspectral sensitizer for fogged direct positive emulsions givingdensities of 1.70 and 0.03 for the unexposed and exposed areas,respectively, with a maximum sensitivity at 550 nm. and a relative speedof 1100.

EXAMPLE 26 6 chloro-2-{2-[6-( 4 nitrophenylimidazo[2,l-b]thiazol- 5-yl]vinyl}- 1 ,S-diphenylimidazo [4,5 -b] quinoxalinium p-toluene sulfonate9H5 s/\ N N N Cl y N CH=CH N02 s 0=C H This compound is prepared in amanner similar to Examples 24 and 25; yield 2.03 g. (51%). The dye ispurified by recrystallization from methanol (350 ml.); yield 0.57 g.(14%), M.P. 312-315 C., decomposes.

This dye containing the desensitizing imidazo[4,5-b] quinoxaline nucleusshows (Table 1 hereinafter) densities of 1.86 and 0.04 for the unexposedand exposed areas, respectively, with a maximum sensitivity at 575 nm.and a relative speed 1050, as tested by the procedure of aboveExample 1. These results indicate that this dye also is an outstandingelectron acceptor and spectral sensitizer for fogged direct positiveemulsions.

In place of the intermediates employed in above Examples 24, 25 and 26,there can be substituted an equivalent amount of any other of thosedefined by Formulas III and IV above to give the corresponding dyeshaving generally similar reversal and spectral sensitizing propertiesfor direct positive photographic emulsions. For example, by appropriateselections of intermediates, the following dyes can be readily prepared:the dye 3-alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl,etc.)-2-{2- [6-(4-nitrophenyl)imidazo[2,1 b]thiazol yl]vinyl}-6-nitrobenzothiazolium salt (e.g., the chloride, bromide, iodide,perchlorate, p-toluenesulfonate, etc. salt; the dye 3-alkyl (e.g.,methyl, ethyl, propyl, isopropyl, butyl, decyl, etc.) 2{2-[6-(4-nitrophenyl)imidazo[2,l-b]thiazol-5-yl]vinyl}-6-nitrobenzoxazolium salt (e.g., the chloride, bromide,iodide, perchlorate, p-toluenesulfonate, etc. salt); the dye 3-alkyl(e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl,etc.)-2-{2-[6-(4-nitrophenyl)imidazo[2,1-b]selenaziol 5yl]vinyl}-6-nitrobenzoselenazolium salt (e.g., chloride,p-toluenesulfonate, etc. salt); the dye2-[2-(6-phenylimidazo[2,l-blthiazol 5 yl)vinyl]-1,3-diphenylimidazo[4,5-b]quinoxalinium salt (e.g., the chloride,bromide, iodide, perchlorate, p-toluenesulfonate, etc. salt); and thelike dyes.

The following Examples 27 and 28 illustrate the preparation ofimidazo[2,1-b]thiazole intermediates defined by Formula IV above.

EXAMPLE 27 6- (4-nitrophenyl) imidazo [2, l-b] thiazole 2-aminothiazole(10.01 g., 1 mol.), 2-bromo-4'-nitroacetophenone (24.40 g., 1 mol.) andsodium carbonate (5.30 g., 0.5 mol.) in ethanol (100 ml.) are stirredfor 24 hours at room temperature. The tan precipitate is collected bysuction filtration, washed twice with distilled water (500 ml.) anddried in vacuo at C. for 4 hours; yield 22.7 g. (93%), M.P. l8l-l88 C.The product is purified by recrystallization from ethanol (750 ml.);yield 5.78 g. (24%), M.P. 269-272-C. [lit. M.P. 283-4 C.; T. Matsukawaand S. Ban, J. Pharm. Soc. Japan, 71, 756-9 (1951); CA, 46, 8094(1952)].

EXAMPLE 28 5-formyl-6- (4-nitrophenyl) imidazo 2, l-b] thiazole6-(4-nitrophenyl)imidazo[2,l-b]thiazole (9.32 g., 1 mol.) is dissolvedin dimethylformamide (150 m1.) and added rapidly to a solution ofphosphoryl chloride (5 ml.) in dimethylformamide (15 ml.) at ice bathtemperature. The reaction mixture is heated on a steam bath for 1 hr.,chilled, added to 370 g. of crushed ice, treated with aqueous sodiumhydroxide (27.0 g., 50% heated to C. and chilled. The grayish-brownprecipitate is collected by suction filtration, washed with distilledwater (300 ml.) and dried; yield 9.37 g. (90%), M.P. 248 C. The aldehydeis purified by recrystallization from acetone (2250 ml.); yield 4.25 g.(41%), M.P. 255-256 C., dec.

It will be apparent that other intermediates defined by Formula IV abovecan be prepared by appropriate substitutions of the starting reactantsin the procedures of above Examples 27 and 28.

The preparation of the highly useful polymethine dyes of the inventionderived from imidazo[2,l-b]-l,3,4-thiadiazoles, and intermediatestherefor, is illustrated by the following examples.

EXAMPLE 29 1,3,3-trimethyl-2-{2-[2 methyl 6 (4-nitrophenyl)imidazo[2,1b]-l,3,4-thiadiazol 5 yl]vinyl}-5-nitro-3H- indolium p-toluenesulfonateCH: OH;

5-formyl 2 methyl-6-(4-nitrophenyl)imidazo[2,1-b]- 1,3,4-thiadiazole(1.00 g.; 1 mol.) and 1,2,3,3-tetramethyl-5-nitro-3H-indoliump-toluenesulfonate (1.37 g., 1 mol.) in acetic anhydride (25 ml.) arerefluxed for 5 minutes. The cooled reaction mixture is added to ether-(500 ml.), stirred and filtered; the precipitate is suspended in ether(500 ml.), recovered by filtration, Washed with ether and dried; yield1.93 g. (84%). The dye is purified by recrystallization fromacetonitrile/acetone, yield 0.26 g. (11%), M.P. 232 C., dec.

The above prepared dye containing the desensitizing1,3,3-trimethyl-5-nitro-3H-indole nucleus is tested by the procedure ofabove Example 1. The results shown in Table 1 hereinafter indicate thisdye to be an excellent electron acceptor and spectral sensitizer forfogged direct positive emulsions. The densities are 1.88 and 0:09 forthe unexposed and exposed areas, respectively, with a maximumsensitivity at 560 nm. and a relative speed of 1000.

EXAMPLE 30 3-ethyl-2-{2-[2-methyl 6 (4nitrophenyl)imidazo[2,1-

b]-1,3,4 thiadiazol-S-yl]vinyl}-6-nitrobeuzothiazoliump-toluenesulfonate N// N\ 011-011 No:

This compound is prepared in a manner similar to Example 29; yield 1.71g. (73%). The dye is purified by recrystallization from ethanol (1.31.); yield 0.50 g. (21%), M.P. 269-270 C., dec.

This dye containing the desensitizing 3-ethyl-6-nitro- 5 benzothiazolenucleus is an excellent electron acceptor and spectral sensitizer forfogged direct positive photographic emulsions as indicated by the valueslisted in Table 1 hereinafter. Referring to the table, it will be seenthat the densities for this dye are 1.90 and 0.05 for the unexposed 30and exposed areas, respectively, the maximum sensitivity is 545 nm. andthe relative speed is 955.

EXAMPLE 31 1,3 diethyl 2 {2-[2-methyl-6-(4-nitrophenyl) imidazo- Thisdye is made in a manner similar to Examples 29 and 30; yield 1.52 g.(64% The compound is purified 'by recrystallization fromacetonitrile/acetone; yield 0.32 g. (13%), M.P. 278-280 C., dec.

This dye containing the desensitizing1,3-diethylimidazo[4,-b]quinoxaline nucleus qualifies as an excellentelectron acceptor and spectral sensitizer for fogged direct positiveemulsions shown in Table 1 hereinafter, densities of 1.78 and 0.05 forthe unexposed and exposed areas, respectively, with a maximumsensitivity of 535 nm. and a relative speed of 871.

In place of the intermediates employed in above Examples 29, 30 and 31,there can be substituted an equivalent amount of any other of thosedefined by Formulas HI and IV above to give the corresponding dyeshaving generally similar reversal and spectral sensitizing propertiesfor direct positive photographic emulsions. For example, by appropriateselections of intermediates, the following dyes can be readily prepared:the dye 3-alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl,etc.)-2-{2-[2-methyl- 6-(4-nitrophenyl)imidazo[2,1-b] 1,3,4thiadiazol-S-yl] vinyl}-6-nitrobenzothiazolium salt (e.g., the chloride,bro mide, iodide, perchlorate, p-toluenesulfonate, etc. salt); the dye3-alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl, etc.) 2{2 [2 methyl 6-(4-nitrophenyl) imidazo [2,1-b] 1,3,4 thiadiozol 5yl]vinyl}-6-nitrolaenzoxazolium salt (e.g., the chloride, bromide,iodide,

22 perchlorate, p-toluenesulfonate, etc. salt); the dye 2-[2-(6-phenylimidazo[2,-b] 1,3,4 thiadiazol 5 y1)vinyl]-1,3-diphenylimidazo[4,5-b]quinoxalinium salt (e.g., the chloride, bromide,iodide, perchlorate, p-toluenesulfonate, etc. salt); and the like dyes.

The following Examples 32 and 33 illustrate the preparation ofimidazo[2,l-b] 1,3,4 thiadiazole intermediates defined by Formula IVabove.

EXAMPLE 32 2-methyl-6-(4-nitrophenyl)imidazo[2,1-b]-l,3,4- thiadiazole Ni G CH3 A NO;

2 amino 5 methyl-1,3,4-thiadiazole (5.80 g., 1 mol.) andZ-bromo-4'-nitroacetophenone (12.20 g., 1 mol.) in ethanol (200 ml.) arerefluxed for 30 minutes. The hot reaction mixture is filtered to obtaina yellow precipitate which is dried in vacuo at C.; yield 14.45 g. (80%)of the hydrobromide salt, M.P. 234236 C. The precipitate is suspended indistilled water (775 ml.) and refluxed for one hour; the hot reactionmixture is filtered to obtain a yellow precipitate which is dried invacuo at C.; yield 9.26 g. (71% M.P. 243 -245 C. [lit. M.P. 241 242 C.,T. Matsukawa and S. Ban., J. Pharm. Soc. Japan, 72, 6104 (1952); CA, 47,6409 (1953)].

EXAMPLE 33 5-formyl-2-methyl-6-(4-nitrophenyl)imidazo-[2,l-b]-l,3,4-thiadiazole 2-methyl 6 (4nit-rophenyl)imidazo[2,1-b]-1,3,4- thiadiazole (13.00 g., 1 mol.) issuspended in dimethylformamide and added rapidly to a solution ofphosphoryl chloride. (5.04 ml.) in dimethylformamide (15 ml.) at icebath temperature. The reaction mixture is heated on steam bath for 2hours, chilled, added to 370 g. of crushed ice, treated with aqueoussodium hydroxide (27.0 g., 50% heated to 90 C. and chilled. The tanprecipitate is collected by suction filtration, washed with distilledwater and dried; yield 13.15 g. (91% The aldehyde is purified byrecrystallization from ethanol (2 1.); yield, 6.61 g. (46%), M.P. 189 C.

It will be apparent that other intermediates defined by Formula IV abovecanbe prepared by appropriate substitutions of the reactants in theprocedures of above Examples 32 and 33.

The preparation of the highly useful polymethine dyes of the inventionderived from imidazo[1,2-b]pyridazines, and intermediates therefor, isillustrated by the following examples.

EXAMPLE 34 2 {2 [2 (4 bromophenyl) 6 chloroimidazo[1,2-b] pyridazin 3yl]vinyl}-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate2-(4-bromophenyl) 6 chloro-3-formylimidazo[1,2-b] pyridine (1.38 g., 1mol.) and 3-ethyl-2-methyl-6-nitro benzothiazolium p-toluenesulfonate(1.62 g., 1 mol.) in acetic anhydride (20 ml.) are refluxed for 2minutes. The cooled reaction mixture is added to ether (1 1.), stirredand filtered; the precipitate is purified by recrystallization frommethanol/ ethanol; yield 0.89 g. (30% M.P. 270- 272 C., dec.

The above prepared dye containing the desensitizing 3-ethyl-6-nitrobenzothiazole nucleus is tested by the procedure of aboutExample 1. The results as shown in Table 1 hereinafter indicate thatthis dye is a good quality, excellent electron acceptor and spectralsensitizer for fogged direct positive photographic emulsions. It givesdensities of 1.74 and 0.09 for the unexposed and exposed areas,respectively, with a maximum sensitivity at 555 nm. and a relative speedof 525.

EXAMPLE 35 2-{2-[2-(4-brornophenyl) 6 chlorimidazo[1,2-b]pyridazin-3-yl]vinyl} 1,3 diethylimidazio[3,5 b]quinoxaliniump-toluenesulfonate N CH==CH oso c H I 1 7 l Br 2-(4-bromophenyl) 6chloro-3-formylimidazo[1,2-b] pyridazine (1.38 g., 1 mol.) andl,3-diethyl-2-methylimidazo[4,5-b]quinoxalinium p'toluenesulfonate (169g., 1 mol.) in acetic anhydride (20 ml.) are refluxed for 2 minutes. Thecooled reaction mixture is added to ether (1 1.), stirred and filtered;the precipitate is washed with ether and dried; yield 2.01 g. (67% Thedye is purified by recrystallization from ethanol; yield 0.76 g. (25%),M.P. 289-291" C., dec.

The exact photographic test procedure described in above Example 1 iscarried out with the above prepared dye which contains the desensitizing1,3-diet-hylimidazo [4,5-b]quinoxaline nucleus. The results are recordedin Table 1 hereinafter. Referring to the table, the densities are shownto be 1.54 and 0.06 for the unexposed and exposed areas, respectively,the maximum sensitivity is at 520 nm. and the relative speed is 457.Accordingly, this dye is a good electron acceptor and spectralsensitizer for fog-ged direct positive emulsions.

EXAMPLE 36 2-{2-[2-(4-bromophenyl) 6 methoxyimidazo[1,2-b]

pyridazin-3-yl]vinyl} 1,3,3 trimethyl 5 nitro-3H- indoliump-toluenesulfonate CH3 CH! N N N02 CH=CH 2-(4-bromophenyl) 3 formyl -6methoxyimidazo [1,2-b]pyridazine (2.00 g., 1 mol.) and1,2,3,3tetramethyl--nitro-3'H-indolium p-toluenesulfonate in aceticanhydride (25 ml.) are refluxed for 15 minutes. The cooled reactionmixture is added to ether (600 ml.), stirred and 24 filtered; theprecipitate is washed with ether and dried; yield 3.53 g. (83%). The dyeis purified by recrystallization from ethanol; yield 2.24 g. (53%), M.P.264266 C., dec.

The above prepared dye containing the desensitizing1,3,3-trimethyl-5-nitro-3H-indole nucleus is photographically tested bythe exact procedure described in above Example 1. The results as shownin Table 1 hereinafter indicate that this dye is a very good qualityelectron acceptor and spectral sensitizer for fogged direct positiveemulsions. Densities are shown to be 1.64 and 0.12 for the unexposed andexposed areas, respectively, the maximum sensitivity is at 558 nm. andthe relative speed is 955.

EXAMPLE 37 2-{2- [2-(4bromophenyl) 6 chloroimidazo[l,2-b]pyridazin 3yl]vinyl}-1,3,3-trimethyl-5-nitro-3H-indolium p-toluenesulfonate 2-(4bromophenyl) 6 chloro 3 formylimidazo ['1,2-'b]pyridazine (1.38 g., 1mol.) and 1,2,3,3-tetramethyl-5-nitro-3H-indolium p-toluenesulfonate inacetic anhydride (20 ml.) are refluxed for 10 minutes. The cooledreaction mixture is added to ether (1 l.) stirred and filtered; theprecipitate is washed with ether and dried; yield 2.21 g. (86% The dyeis purified by recrystallization from ethanol; yield 1.17 g. (42%), M.P.244-245 C., dec.

This dye containing the desensitizing nucleus1,3,3-trimethyl-5-nitro-3H-indole nucleus is tested by the procedure ofabove Example 1. The results are listed in Table 1 hereinafter.Referring to the table, it will be seen that the densities are 1.74 and0.12 for the unexposed and exposed areas, respectively, the maximumsensitivity is at 540 nm. and the relative speed is 631. Accordingly,this dye qualifies as a good electron acceptor and spectral sensitizerfor fogged direct positive emulsions.

EXAMPLE 38 2-{2-[2-(4-bromophenyl) 6 methoxyimidazo[l,2 b]

pyridazin 3 yl]vinyl}-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate2-(4-bromophenyl) 3 formyl 6 methoxyimidazo- [1,2-b]pyridazine (2.00 g.,1 mol.) and 3-ethyl-2-methyl- 6-nitrob-enzothiazolium p-toluenesulfonate(2.37 g., 1 mol.) in acetic anhydride (25 ml.) are refluxed for 3minutes. The cooled reaction mixture is added to ether (500 ml.),stirred and filtered; the precipitate is washed with ether and dried;yield 3.45 g.'(85%). The dye is recrystallized from chloroform; yield2.16 g. (53%), M.P. 279-281" C., dec.

The exact photographic test procedure of above Example 1 is carried outwith the above dye which contains the desensitizing1-ethyl-6-nitrobenzothiazole nucleus. The results are recorded in Table1 hereinafter. The table shows densities of 1.70 and 0.07 for theunexposed and exposed areas, respectively, with a maximum sensitivity at550 nm. and a relative speed of 725. This dye is, therefore, consideredas being an excellent electron acceptor and spectral sensitizer forfogged direct positive emulsions.

EXAMPLE 39 2-{2-[2-(4-bromophenyl-6-methoxyimidazo[1,2 b]pyridazin 3yl]vinyl} 1,3 diethylimidazo[4,5 b]quinoxalinium p-toluenesulfonate2-(4-bromophenyl) 3 formyl 6 methoxyimidazo- [1,2-b]pyridazine (2.00 g.,1 mol.) and 1,3-diethyl-2- methylimidazo[4,5-b]quinoxalinium ptoluenesulfonate (2.47 g., 1 mol.) in acetic anhydride (25 ml.) arerefluxed for 2 minutes. The cooled reaction mixture is added to ether(500 ml.), stirred and filtered; the precipitate is washed with etherand dried; yield 2.96 g. (68%). The dye is purified by recrystallizationfrom ethanol; yield 0.81 g. (18%), M.P. 284286 C., dec.

The above prepared dye containing the desensitizing1,3-diethylimidazo[4,5-b]quinoxaline nucleus is photographically testedby the procedure described in above Example 1. The results are set forthin Table 1 hereinafter. Referring to the table, it will be seen that thedensities obtained with this dye are 1.68 and 0.05 for the unexposed andexposed areas, respectively, with a maximum sensitivity at 530 nm. and arelative speed of 832. Accordingly, this dye is an excellent electronacceptor and spectral sensitizer for fogged direct positive emulsions.

In place of the intermediates employed in above Examples 34 to 39, therecan be substituted an equivalent amount of any other of those defined byFormulas III and IV above to give the corresponding dyes havinggenerally similar reversal and spectral sensitizing properties fordirect positive photographic emulsions. For example, by appropriateselections of intermediates, the following dyes can be readily prepared:the dye 2 {2 [2 (4-chlorophenyl)-6-chloroimidazo[l,2-b]pyridazin 3yl]vinyl}- 3-alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl,decyl, etc.) 6 nitrobenzothiazolium salt (e.g., the chloride, bromide,iodide, perchlorate, p-toluenesulfonate, etc. salt); the dye 2-{2- [2-(4-bromophenyl)-6-methoxyimidazo [1,2-b]pyridazin-3-yl]vinyl}-3-alkyl(e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl,etc.)-6-nitrobenzoxazolium salt (e.g., the chloride, bromide, iodide,perchlorate, ptoluenesulfonate, etc. salt); the dye2-{2-[2-(4-bromophenyl)-6-chloroimidazo[l,'2-b]pyridazin 3 yl]vinyl}-1,3 diphenylimidazo[4,5-b]quinoxalinium salt (e.g., the chloride,bromide, iodide, perchlorate, p-toluenesulfonate, etc. salt); and thelike dyes.

The following Examples 40 to 43 illustrate the preparation ofimidaZo[l,2-b]pyridazine intermediates defined by Formula IV above.

26 EXAMPLE 40 2- (4-bromophenyl) -6-chloroimidazo 1,2-b pyridazine3-amino-6-chloropyridazine (5.78 g., 1 mol.) and a,pdibromoacetophenone(13.9 g., 1 mol.) in ethanol (150 ml.) are refluxed for 3 hrs. Thecooled reaction mixture is filtered to obtain a colorless precipitate;yield 6.93 g. (45% M.P. 220222 C. (lit. M.P. 222 C.) [C.A., 64, 3566(1966), Japan, 22,264 (1965)].

EXAMPLE 41 2- (4-bromophenyl) -6-methoxyimidazo 1,2-b] pyridazinecum-@111 3-amino-6-methoxypyridazine (12.50 g., 1 mol.) anda,p-dibromoacetophenone (5.63 g., 1 mol.) in ethanol (150 ml.) arerefluxed for 2 hrs. The cooled reaction mixture is filtered to obtain acolorless precipitate; yield 11.96 g. (87% M.P.197199 C.

EXAMPLE 42 2- (4bromophenyl) -6-chloro-3-formylimidazo 1,2-b] pyridazineCHO A mixture of 2-(4-brom0phenyl)-6-chloroimidazo[1,2- b]pyridazine(6.93 g., 1 mol.) in hot dimethylformamide (75 ml.) is added slowly to asolution of phosphoryl chloride (2.5 ml.) and dimethylformamide (15 ml.)at ice bath temperature. The reaction mixture is heated on a steam bathfor 1 hr., cooled, added with stirring to 370 g. of crushed ice, treatedwith aqueous sodium hydroxide (50%, 27.0 g.), heated to 90 C., cooledand filtered. The precipitate is resuspended in water (500 ml.),recovered by suction filtration and dried; yield 6.96 g. (94%). Thealdehyde is purified by recrystallization from chloroform/ ethanol;yield 4.65 g. (63%), M.P. 194l97 C.

EXAMPLE 43 2-(4-bromophenyl)-3 -formyl-6-methoxyimidazo [1,2-b]pyridazine CHO N cmo This compound is prepared in a manner similar tothat described for Example 42. The yield is 6. 82 g. (79%), M.P. 153-156C.

It will be apparent that other intermediates defined by Formula IV abovecan be prepared by appropriate substitutions of reactants in theprocedures of above Example 40 to 43.

The effectiveness of the dyes of the above examples as electronacceptors and spectral sensitizers for fogged direct positivephotographic emulsions is determined by the exact procedure described inabove Example 1. The results are listed in the following table.

TABLE I Density Dye of Dye conc., Relative Max. un- Min.

g./mole clear exposed exposed sensitizing silver speed areas areas max.(nm.)

0. 45 339 1. 87 0. 12 550 0. 45 468 1. 91 0. 550 0. 96 138 1. 43 0. 13Blue 0. 45 50 1. 80 0. 72 Blue 0. 70 575 1. 96 0. 02 585 0. 70 692 1. 980. 02 560 0. 75 1, 050 1. 74 0. 04 595 0. 50 955 1. 88 0. O4 580 0. 75603 1. 68 0. 12 580 0.75 501 1. 64 0. 586 0. 75 550 1. 72 0. 08 580 0.75 1, 380 1. 92 0. 03 575 0. 75 1, 510 1. 84 O. 06 600 0. 75 1, 200 1.93 0.06 590 0. 50 832 1. 82 0. 04 580 0. 75 1, 100 1. 70 0. 03 550 0. 751, 050 1. 86 0. 04 575 0. 75 1, 000 1. 88 0. 09 560 0. 50 955 1. 90 0.05 545 0. 75 871 1. 78 0. 05 535 0. 50 525 1. 74 0. 09 555 0. 75 457 1.54 0. 06 520 0. 75 955 1. 64 0. 12 558 0. 50 631 1. 74 0. 12 540 0. 50725 1. 70 0. 07 550 0. 75 832 1. 68 0. 05 530 0. 00 1 1. 90 N0 reversalThe following examples further illustrate the preparation of fogged,direct positive photographic emulsions and elements with the dyes of theinvention.

EXAMPLE 44 Grams N-methyl-p-aminophenol sulfate 3.1 Sodium sulfite, des45 Hydroquinone 12 Sodium carbonate, des. 67.5 Potassium bromide 1.9

Water to 1 liter.

The light fog-ged material can be exposed to an image with lightmodulated by a Wratten No. 15 cfilter to give a direct positive image.Generally similar results are obtained when the dyes of Examples 7, 24,25 and 26 are used in place of the above dye.

EXAMPLE 45 Seven pounds of a silver chloride gelatin emulsion containingthe equivalent of 100 g. of silver nitrate is heated to 40 C. and the pHis adjusted to 7.8. Eight cc. of full strength (40%) formalin solutionis added and the emulsion is held at 40 C. for 10 minutes. At the end ofthe holding period, the pH is adjusted to 6.0 and 0.125 g. of 6 chloro2-{2- [7-methy1-2-(4-nitrophenyl)imidazo- [1,2 a]pyrid 3yl]vinyl}-1,3-diphenylimidazo[4,5-b] quinoxalinium iodide (Example 13).The emulsion is coated on a support, and provides good direct positiveimages. Similar results are obtained when the dyes of Examples 12, and14, 29, 30, 31, 38 and 39 are substituted for the above dye.

By substituting other dye compounds of the invention, as defined inFormulas I and II above, into the procedure of the above examples,similar fogged, direct positive photographic silver halide emulsions andphotographic elements may be prepared.

The photographic silver halide emulsion and other layers present in thephotographic elements made according to the invention can be hardenedwith any suitable hardener, including aldehyde hardeners such asformaldehyde, and mucochloric acid, aziridine hardeners, hardeners whichare derivatives of dioxane, oxypolysaccharities such as oxy starch oroxy plant gums, and the like. The emulsion layers can also containadditional additives, particularly those known to be beneficial inphotographic emulsions, including, for example, lubrieating materials,stabilizers, speed increasing materials, absorbing dyes, plasticizersand the like. These photographic emulsions can also contain in somecases additional spectral sensitizing dyes. Furthermore, these emulsionscan contain color forming couplers or can be developed in solutionscontaining couplers or other color generating materials. Among theuseful color formers are the monomeric and polymeric color formers,e.g., pyrazolone color formers, as well as phenolic, heterocyclic andopen chain couplers having a reactive methylene group. The color formingcouplers can be in corporated into the direct positive photographicsilver halide emulsion using any suitable technique, e.g., techniques ofthe type shown in Jelley et al. US. Pat. 2,322,027, issued June 15,1943, Fierke et al. US. Pat. 2,801,171, issued July 30, 1957, FisherU.S. Pats. 1,055,155 and 1,102,028, issued Mar. 4, 1913 and June 30,1014, respectively, and Wilmanns US. Pat. 2,186,849 issued Jan. 9, 1940.They can also be developed using incorporated developers such aspolyhydroxyhenzenes, aminophenols, 3-pyrazolidones, and the like.

Although the invention has been described in considerable detail withparticular reference to certain preferred embodiments thereof, it willbe understood that variations and modifications can be effected withinthe spirit and scope of the invention as described hereinabove, and asdefined in the appended claims.

We claim:

1. A polymethine dye selected from those having one of the followinggeneral formulas:

wherein n represents a positive integer of 1 or 2; L represents amethine linkage; R represents a member selected from the groupconsisting of a hydrogen atom, an alkyl group of 1 to 12 carbon atomsand an aryl group of 6 to 10 carbon atoms; R and R each represents amember selected from the group consisting of an alkyl group of 1 to 12carbon atoms, a lower alkenyl group, a lower alkoxyalkyl group, a lowerhydroxyalkyl group, a lower carboxyalkyl group, a lower sulfoalkylgroup, a lower sulfatoalkyl group, a lower acyloxyalkyl group, a loweralkoxycarbonylalkyl group, and an aryl group of 6 to 10 carbon atoms; Zrepresents the non-metallic atoms necessary to complete a desenitizingnucleus selected from the group consisting of a nitrobenzothiazolenucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, aimidazo[4,5-b]quinoxaline nucleus, a 1,3-dialkenylimidazo-[4,5-b]quinoxaline nucleus, a 1,3-diarylimidazo[4,5-b] quinoxalinenucleus, a 3,3-dialkyl-3H-pyrrolo[2,3-b] pyridine nucleus, a3,3-dialkyl-3H-nitroindole nucleus, and a thiazolo[4,5-b]quinolinenucleus; X represents an acid anion; and Q represents the non-metallicatoms required to complete a fused heterocyclic ring selected from thegroup consisting of an imidazo[1,2-a] pyridine nucleus, animidazo[2,1-b]thiazole nucleus, an imidazo[2,1-b]-1,3,4- thiadiazolenucleus and an imidazo[1,2-b] pyridazine nucleus.

@ 3 3 Q UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3, 9 9l 'Dated y 7, 97

Invencofls) James W. Carpenter, John D. Mee and Donald W. Heseltine Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 71, after "by" the word "both" was omitted. .1

Column 2, line 35, "[2,1-a1" should read '--[2,1-b]--.

Column 3, line 50, "5-phenylselenaz oe" should read --5phenylselenazole--.

Column l, line 5, that part of structure which reads "C-CO" should read-C-C.HO-.--.

Column 8, line 25, "3ethyl6-nitro-2- [2(-phenylimidazo" should read-3-ethyl6-nitro-2-[2-(2-phenylimidazo.

Column)ll, line 2 4, (1. 41 g. 1 mol. should read "(1A1 g. .l 0

Column 11, line M2, "cholride" should read chloride.

- Column l -L, Example 13, that part of structure which reads "CH3"should read H3 NH2 v 10 Page 2 mg UNITED STATES PATENT OFF ICE YCERTIFICATE OF CORRECTION V Patent No. 3, 9, 9 Dated y 7, 19WLInven'tofls) James W. Carpenter, John D. Mee and Donald W. Heseltine Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

C olumn 16, line 52, 'cholride" should read -chloride--. "1 001mm 21,line 5U, "azo[ -L,-b]"should read --azo[ L,5-b]- Column 22, line 2,"phenylimidazo[2,b]" should read --phenylimidazo[2,l-b]--.

Column 23, line ll, "about" should read --above-.

Column 23, line 2 1,,f'dzge thylynidezg[3,5- Should read--diethylimidazo [4,44

Column 29, line 31, [2-(2-phenylimdizo[l,2-a'] should read [2-(2-phenylimidazo[l,2-a]-.

Signed and sealed this 29th day of October 1974.

SEAL Attest: v McCOY M. GIBSON JR. C. MARSHALL DANN- Attesting OfficerCommissioner of Patents

